Final answer:
The self-splicing Group II introns are structural RNA elements forming complex stem-loop configurations that can catalyze their own excision without additional proteins or cofactors, creating lariat structures in the process.
Step-by-step explanation:
Structure and Splicing of Group II Introns
The structure of self-splicing Group II introns consists of complex stem-loop tertiary formations. The splicing of these introns is a self-splicing mechanism that occurs without the need for external cofactors or proteins. A notable feature is the 2'-hydroxyl group of an adenylate residue within the intron that initiates the reaction. This results in the formation of an unusual branched lariat structure at an A residue branch site. This lariat has a 2',5'-phosphodiester bond and is similar to the lariat structure formed by spliceosomal intron splicing, suggesting that spliceosomal splicing may have evolved from mechanisms akin to those of Group II introns.
In summarization, splicing involves the precise removal of introns from a pre-mRNA transcript, with Group II introns being capable of self-splicing, forming lariat structures during the process which then lead to the excision of the intron and the joining of the exons.